1. Field of the Invention
The present invention is related to flame retardants. More particularly, the present invention is related to flame retardants comprising both aliphatic and aromatic bromine for use with styrenic resins.
2. Description of Related Art
Styrenic resins are well known in the synthetic organic polymer art as a class of thermoplastics that offer excellent mechanical properties as well as good chemical resistance. The properties that make styrenics useful for many applications as solid polymers also make them very desirable as foamed polymers. A number of processes have been developed over the last forty years to prepare styrenic foams for a variety of applications, some of which require the use of flame retardants.
A flame retardant, such as a halogenated organic compound, is often incorporated into a formulated resin in order to render the resin resistant to ignition. It is known that brominated aliphatic compounds, brominated aromatic compounds, and mixtures thereof have been used in solid and foamed styrenic applications. Hexabromocyclododecane (HBCD) is one such known aliphatic brominated flame retardant that has been used in foamed styrenic applications. HBCD is a highly brominated aliphatic flame retardant that has unusually high thermal stability, which results in excellent performance at low loading levels with a minimum effect on polymer properties.
Recently there have been concerns about the health and environmental impact of some flame retardants including HBCD. Although scientific studies have not necessarily shown significant risks to human health or the environment, there are ongoing reviews by various regulatory agencies that may result in reduced usage of HBCD. In the event that these agencies limit the usage of HBCD, extruded polystyrene foam and expanded polystyrene foam manufacturers may be required to choose an alternative flame retardant, and many may adopt a substitute before any regulatory mandate. Thus, there exists a need for a flame retardant alternative to HBCD that is more environmentally friendly and maintains all of the performance properties of HBCD.
WO 2007/057900 discloses polybrominated bisaryl compounds containing bromomethyl or bromomethylene groups, as well as flameproof polymeric formulations comprising the compounds. These compounds are said to exhibit good thermal stability and to be particularly suitable for flame-retarding polystyrene thermoplastic foams. A process for making the polybrominated bisaryl compounds is also disclosed.
WO 2006/008738 discloses a process for the preparation of highly pure pentabromobenzyl bromide, wherein the benzylic bromination reaction is carried out in a suitable organic solvent in the presence of water and wherein the reaction temperature is such that it is sufficient to activate the initiator but not high enough to consume a substantial amount thereof.
WO 2006/013554 discloses a styrenic polymer composition comprising a flame-retardant effective amount of a compound of formula (I): (C6H(5-n)Yn)CH2X, wherein X is Cl or Br; Y is Cl or Br; and n is an integer between 1 and 5; or a mixture of two or more of said compounds of formula (I) or their homologues and derivatives or other Br—FRs.
GB 1,107,283 discloses a granular expandable polystyrene composition that contains as a fire-retardant a minor amount of a compound of formula Ar(Br)m(Cl)nR or Ar(Br)x(Cl)yOR where Ar is an aryl residue, m is 1-4, n is 0-2, x is 1 or more, y is 0 or an integer and R is hydrogen, a straight or branched chain alkyl group which may be halogenated, a straight or branched chain alkenyl group or a halogenated aryl group; there being at least 2 nuclear bromine atoms per molecule of the above compound. The compound may be tetrabromobenzene, tribromophenol, pentabromophenyl (allyl, ethyl or n-propyl)ether, an isomer of tribromotoluene or tribromophenyl allyl ether, chlorodibromotoluene, chlorodibromophenyl allyl ether, hexabromodiphenyl ether, dibromodiphenyl, dibromonaphthalene; 2,4-dibromo-1-methylnaphthalene; 1,5-dibromoanthracene; pentabromophenyl dibromopropyl ether, pentabromophenol or tetrabromochlorophenol. The composition may also contain dicumyl or di-tert. butyl peroxide, tert. butyl peracetate or cumene hydroperoxide. The compositions may be made by polymerizing styrene in the presence of the fire-retardant compound, polystyrene granules, benzoyl peroxide, water and petroleum ether as expanding agent and the resulting polymer may be granulated, expanded by heating in steam and then moulded into a block.
GB 1,394,787 discloses a flame resistant polystyrene or styrene-containing copolymer containing hexabromoxylene. There is further disclosed a self-extinguishing mouldable composition or moulding comprising polystyrene or a styrene-containing copolymers and hexabromoxylene in an amount of from 0.5 to 8.0 percent by weight, based on the total weight of the mould able composition or moulding.
EP 0502333 discloses a process for preparing a mixture of brominated, non-condensed ring polyaromatics, which process comprises brominating the precursor non-condensed ring polyaromatic in the presence of a bromination catalyst. The mixture has an average bromine number of 5.8 to 6.2, more than about 55 GC area percent of the hexabromo homolog, and a reduced amount of light-end impurities.
U.S. Pat. No. 4,024,092 discloses polymer compositions having enhanced oxygen index values as measured by ASTM Method D-2863-70, which compositions contain effective amounts of a bromo or chloro derivative of stilbene.
U.S. Pat. No. 5,039,729 discloses mixtures of brominated diphenyl ethanes, such mixtures containing a predominant amount of hexabromodiphenyl ethane and having an average bromine number, based upon GC area percent, of from about 6.7 to about 7.3. ABS based formulations containing such mixtures and articles made from such formulations are also disclosed.
U.S. Pat. No. 5,055,235 discloses a process for preparing a mixture of brominated, non-condensed ring polyaromatics, which process features multiple bromination temperatures and multiple catalyst additions for brominating the precursor non-condensed ring polyaromatic. The mixture has an average bromine number of about 6 to about 8 bromine atoms per molecule, a low melting point range, and a low amount of light end impurities.
U.S. Pat. Nos. 5,741,949 and 6,117,371 disclose a process for producing a brominated, non-fused aromatic composition that involves a continuous bromination in a continuous, mixed reactor such as a continuous stirred tank reactor. Bromine and the aromatic substrate, and optionally a bromination catalyst, are continuously fed to a reaction zone to form a reaction mixture, and the reaction mixture is continuously withdrawn from the reaction zone after an established average residence time. Bromination levels can be readily controlled by controlling the average residence time of the reaction mixture within the reaction zone. Preferred continuous processes also provide mixed, brominated compositions having product distributions which are substantially broader than that obtained by batch brominations conducted to achieve the same level of bromination. Preferred products thus have broad melting ranges which are advantageous in compounding operations.
U.S. Pat. No. 5,821,393 discloses a process for the preparation of an aromatic bromoalkyl-substituted hydrocarbon compound, in which an alkyl-substituted aromatic hydrocarbon compound is reacted with a brominating agent in the presence of water.
U.S. Pat. No. 6,743,825 discloses an additive mixture said to be useful as a flame retardant. The mixture is comprised of (i) a poly(bromophenyl)alkane having in the molecule in the range of 13 to 60 carbon atoms and in the range of two to four aryl groups and (ii) a poly(bromophenyl)bromoalkane having in the molecule in the range of 13 to 60 carbon atoms and in the range of two to four aryl groups, said poly(bromophenyl)bromoalkane being in an amount which is greater than 25 wt %, based on the total weight of the additive mixture. A process for making the poly(bromophenyl)bromoalkane is also disclosed.
The disclosures of the foregoing are incorporated herein by reference in their entirety.